An HDD (hard disk drive) suspension has been prepared by etching stainless steel foil, and a magnetic head, such as a thin-film inductive head is mounted onto the tip of such suspension and wire bonded with gold wire. In recent years, however, concentrated studies are under way aiming at reduced size, higher density and higher capacity of HDD and, as the studies progress, reduction of flying height of a slider onto which a magnetic head is mounted has become a theme of the utmost importance. From this viewpoint, the conventional gold wires have presented an obstacle to reduction of flying height because of their resistance to air and rigidity. Moreover, wire bonding with such gold wires presents difficulties in automating the step for connecting gold wires with a magnetic head.
As a solution to the problems related to wire bonding with a gold wire, a process such as disclosed in Japan Kokai Tokkyo Koho Sho 60-246015 (1985) proposes to effect patterning with electrically insulating polyimide directly on a stainless steel foil and form a circuit with copper on the polyimide patterns in order to form signal lines directly on a suspension in place of the aforementioned gold wire. A suspension on which signal lines are formed directly in this manner or the so-called integrally-wired suspension does not cause problems of interference with reduction of flying height of a slider due to resistance to air and rigidity of signal lines and also makes it possible to automate the connecting process of a magnetic head.
On the other hand, Japan Kokai Tokkyo Koho Hei 5-131604 (1993) discloses a process for laminating polyimides to a thin metal sheet. However, no attention is paid to the thermal expansion of the polyimides in use and high values of the thermal expansion coefficient concretely disclosed there suggest that deflection tends to occur readily after removal of the metal by etching from the laminate. Moreover, lamination performed as disclosed tends to show variation in adhesive strength between the metal sheet and the polyimide layer and, in addition, gives problematical heat resistance, which makes application of this process difficult to HDD suspensions. Thus, development of materials free of the aforementioned problems was looked for.
Accordingly, an object of this invention is to provide laminates which produce minimal deflection during etching and are suitable for integrally-wired suspensions and to provide a process for preparing said laminates.
After intensive studies of the aforementioned theme, the present inventors have found that the formation of polyimide with specified linear expansion coefficient and adhesive strength on the base material gives laminates suitable for HDD suspensions and completed this invention.